Anymore sudoku variants?...

Just wondering since there's been a bit of activity in these forums recently if people have any ideas for other sudoku variants that they like which aren't already covered?

I think we've got most of them represented here, from the simple variations such as Sudoku X (does anyone see that published anymore - it used to be everywhere?!) through to those that add other rules, such as calcudoku and killer sudoku, and those that add other elements to the solving mix, such as futoshiki and the visually interesting arrow sudoku.

If anyone has any other sudoku variants that they like enough to see in a magazine - either a variants collection or a single-puzzle collection - then share your ideas here, and we'll bear them in mind for future collections